<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app">
    <input type="text" v-model="value">
  </div>
  <script src="lib/vue.js"></script>
  <script>
    var vm = new Vue({
      el: '#app',
      data: {
        value: ''
      },
      watch: {
        value () {
          console.log('侦听器执行了');
        }
      }
    })
  </script>
</body>
</html>